New developments in an eddy current type flaw detector are discussed. Several types of pick‐up units, which contain the exciting coils for inducing eddy currents in the test material and pick‐up coils for detecting changes in this eddy current pattern when a flaw is approached, are described. The electric power for the exciting current is supplied by a vacuum tube power oscillator at a frequency of 500 or 1000 cycles/second. The circuit for detecting the changes in the eddy current pattern employs vacuum tube bridge circuits sensitive to both amplitude and phase changes. The use of jigs to guide the pick‐up unit, automatic scanning, and automatic recording is discussed.